Lobby group Consumer Focus has written to Clydesdale and Yorkshire Banks calling on them to stop demanding cash from mortgage holders as a result of their gaffes.
Many Yorkshire and Clydesdale Bank mortgage holders have reported getting payment demands written off after a computer error meant 18,000 were undercharged for up to two years.
Mortgage holders who owe more than they previously thought due to a lender error may get the shortfall written off if they complain, the Financial Ombudsman Service says.
Yorkshire and Clydesdale Bank mortgage holders who face payment hikes due to their lender's error have been given hope of getting cash back, following two success stories.
Cheap balance transfer credit cards are back in vogue but millions still don't know how to use one properly which has cost them hundreds of pounds a year.